1. Field of the Invention
The present invention relates to an X-ray optical system for small angle scattering to prepare an X-ray beam incident on a specimen in an X-ray small angle scattering apparatus.
2. Description of the Related Art
When an X-ray beam is incident on a specimen, the X-ray scatters with an angle in a range within a small angle (a small angle region) in the vicinity of the travelling direction of the X-ray beam, this being referred to as small angle scattering. Measurement of the small angle scattering provides various pieces of information, including a grain size, a periodic structure and the like, on the specimen material. An apparatus for measuring the above-described small angle scattering is referred to as an X-ray small angle scattering apparatus, and an optical system specific thereto (an optical system for preparing an X-ray beam to be incident on a specimen) is referred to as an X-ray optical system for small angle scattering.
FIG. 8 is a conceptual diagram of the conventional X-ray optical system for small angle scattering. It is noted that, in the drawing, the dimension in the direction perpendicular to the optical axis, the vertical direction in the drawing, is exaggerated. This conventional X-ray optical system for small angle scattering is referred to as a three-slit optical system. The first slit 14, the second slit 16 and the third slit 18 are arranged between an X-ray source 10 and a specimen 12 in the described order from the X-ray source side. An X-ray passing through (or reflected at) the specimen 12 is to scatter and reach an X-ray detector 20. Such a three-slit optical system is disclosed in, for example, Harold P. Klug and Leroy E. Alexander, “X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials”, John Wiley & Sons, 1954, p. 638.
The X-ray optical system for small angle scattering must satisfy the requirements of: a small angle of divergence (for example, 0.04 degree or less) of the X-ray beam incident on the specimen; and a small width W (for example, 0.1 mm or less) of the X-ray beam (direct beam) at a detection point. The first slit 14 and the second slit 16 serve to restrict the angle of divergence of the X-ray beam and to reduce the width of the X-ray beam (direct beam) at the detection point. The third slit 18 serves to interrupt scattered rays from the edge of the second slit 16.
Explaining actual values for realizing the above-described requirements, For example, the aperture width of the first slit 14 is set at 0.04 mm, the aperture width of the second slit 16 is set at 0.03 mm, and the distance L1 between the first slit 14 and the second slit 16 is set at 100 mm.
The above-described three-slit optical system is specific to the X-ray small angle scattering apparatus only, and accordingly a specialized X-ray small angle scattering apparatus must be prepared in order to measure the small angle scattering. Since the three-slit optical system is a special optical system, this cannot be easily switched to other X-ray incident optical systems for X-ray analysis.